As a railway vehicle that travels on a rail, an electric locomotive that drives wheels by an electric motor to travel is generally used. In recent years, there has been suggested a hybrid electric locomotive or an electric diesel locomotive that has an engine and a generator mounted therein, drives the generator using an output from the engine to generate electric power, and supplies the electric power to a main electric motor.
As the hybrid electric locomotive, there is known an electric locomotive having one large engine mounted therein or an electric locomotive having a plural engines and generators mounted therein.
In the hybrid electric locomotive having one large engine, assuming that generated electric power is stored in a storage battery and used, since a vehicle travels by discharging the storage battery, the storage battery must be charged while the vehicle stops or travels until discharge can be performed again. When a high output is required for high-traction or high-speed traveling, the only one mounted engine is fully operated constantly to generate enough traveling power, so the storage battery cannot be sufficiently charged. The storage battery that remains still uncharged and unavailable is equivalent to a so-called dead load that just increases a weight of the vehicle, and it is a factor to deteriorate the powering performance that fundamentally locomotive has.
In the hybrid electric locomotive having medium engines, when the medium engines are operated in accordance with a charged state of the storage battery, the engines must continue operate in a state that is not necessarily optimum for the engines in terms of fuel consumption, an exhaust gas, and others. One engine may be used for power generation and charging. The other engine may be used for traveling of a vehicle.
In this case, if charging is required, one medium engine of the two medium mounted engines is used for charging only. Hence the vehicle cannot get performance that can be obtained from an output from the mounted engines. Conversely, when the two medium engines are used for traveling to assure traveling performance, the storage battery cannot be charged on a permanent basis.
Further, although individually operating the engines in optimum states is desirable, to charge the storage battery by any engine, a large engine must be rotated at a high speed to assure a fixed charging voltage, and noise is produced or fuel consumption deteriorates.